Gating system for electrical musical instrument



Mardl 30 1965 A. J. BlssoNETTE ETA GATING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENT Filed July 1. 1960 2 Sheets-Sheet 1 IN V EN TORS.

Mz. ree Mu/vcn Je.

ATTORNEYS.

United States Patent Office 3,176,060 Patented Mar. 30, 1965 y 3,176,060 GATING SYSTEM FOR ELECTRICAL MUSICAL INSTRUMENT Alfred J. Bissonette, Milford, Ohio, and Walter Munch, Jr., Covington, Ky., assignors to D. H. Baldwin Company, a corporation of Ohio Filed July 1, 1960, Ser. No. 40,232 13 Claims. (Cl. 841.01)

set or pop which can occur if a continuously operating generator is connected with an output system through a simple make-and-break switch. In the prior art, Various means have been employed to eliminate a starting transient in the reproduced tones which would give the effect Vhereinabove, referred to as pop. Resistive switches or gradual contact switches have been found most serviceable, although they involve considerable expense. It is a fundamental object of this invention to provide an inexpensive electrical gating system which, although it employs simple make-and-break key switches, will nevertheless eliminate abrupt initial transients in the tones of electrical musical instruments. In this aspect of the invention, the gating systems taught herein may be employed throughout the organ for all tone derivation purposes.

The gating systems of this invention are also useful in obtaining percussive effects in electrical musical instruments. Percussive effects have to do with the decay of the tone produced by a generator in an output system upon release of a playing key, i.e. the opening of the playing key switch. Where provision is made for a gradual decay of the tone upon release of the key, percussive effects simulating the sounds of bells, bars, struck or plucked strings and the like can be obtained when the instrument is played in a staccato fashion. It is another primary object of the inventionto provide an inexpensive gating system which will produce percussive effects. In this aspect of the invention, the gating systems mayr be adjunctive to the normal make-up of the instrument (i.e. the non-percussive voices may be attained by the usual circuit arrangements); and While in this aspect, the gating system chosen for the obtaining of percussive effects may be built into the original instrument, the systems of this invention are particularly adapted for use as kits enabling the addition of percussive voices to instruments already in use.

The teachings herein are particularly applicable to keying circuits of the type disclosed and claimed in the copending application of Walter Munch, Ir., Serial No. 4,444, entitled Keying System for Electrical Musical Instruments, which application belongs to the same assignee.

The gating systems of this invention are applicable to key-switch-operated instruments of monophonic or polyphonic character and will be described herein in connection with an electrical organ having electronic tone generators, it being understood that this does not constitute a limitation.

As mentioned in the copending application referred to above, which employs small gaseous discharge tubes through which musical tone signals are conducted, there may be a problem of feed-throng when no signals are being passed, due to the small stray capacity across the tubes in the nonconductive state. This may be particularly troublesome in large installations wherein, when no notes are being played, the feed-through, due to the high amplification, becomes objectionable.

In accordance with the principal teachings of the invention, it has been found that a highly satisfactory, economical and reliable gating system may be achieved by employing certain keying systems including some of those disclosed in the copending application referred to above, in a manner such that harmonically (particularly but not necessarily octavely) related tone signals are brought through a common gating valve, which may be a conventional vacuum tube biased in the usual manner to a cut-off, or near cut-off potential. Thus, when one or` more musical tone signals are keyed into the gating valve, a pulsating, uni-directional signal will unblock the gating valve, allowing the signal to pass through. At the same time, any feed-through from unkeyed harmonically-related notes is masked by the components of the tone signal being played. It no tone signal is keyed, the valve remains biased to cut-oif. As will be obvious to one skilled in the art upon reading these specifications, there will be one gating circuit employed for each tone within an octave. In conventional musical instruments employing the equally-tempered scale, there will, of course, be twelve such gating circuits per octave.

It is, therefore, a further object to provide such gating systems wherein objectionable feed-through in high-gain amplification systems is avoided. p

The invention will be described in connection with an electronic mustical instrument such as that set forth in Patent No. 2,233,948, issued March 4, 1941, in the name of Winston E. Kock as inventor. Reference is made to this patent for the details of exemplary generator systems (although others may be used as, for example, the generator system of Patent No. 2,555,038, issued May 29, 1951, in the name of Edward M. Jones), including means for simultaneously deriving octavely related oscillations in different headers and producing voices therefrom by utilizing the outputs of the several headers alone and in combination, means for obtaining voices rich in odd-order haromnics by outphasing, means normally consisting of filter networks for controlling timbre, and for the general organization of an exemplary polyphonic musical instrument. It will be understood, however, that the utility of this invention is not confined to the specific instrument of the said Kock patent, and in particular that the invention may be used with instruments having any type ofgenerating means producing oscillations suitable for use in the production of musical tones.

The objects of the invention set forth above, and others which Will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished in that construction and arrangement of parts of which certain exemplary embodiments will now be described. Reference is made to the accompanying drawings wherein:

FIG. 1 is a diagrammatic circuit representation illustrative merely of the principles of operation of the novel gating system of this invention.

FIG. 2 is a detailed representation of a specific gating circuit such as may be employed in the gating system of FIG. 1.

FIG. 3 is a semi-diagrammatic representation showing the use of two gating systems in such a way that the derived oscillations may be correlated in headers of different footages so that the various modes of obtaining voices outlined in the Kock patent may be employed.

FIG. 4 is a partial diagrammatic showing 'of the use of more than one of the gating systems of this invention, one system at least being arranged to deliver tones simultaneously derived from more than one generator.

Referring now to FIG. 1 of the drawings, there are a series 'of gating circuits indicated as 1, 2, 3, 12, there being one for each tone within an octave, to which are connected, as shown, a series `of oscillators or generators 14, which generate respectively the tones C1, Clif, D1 B1. These generators may, for example, be of the type disclosedin the Jones patent noted above. Also connected to the gating circuits 1, 2, 3, 12, as shown, are another octave of generators indicated at 16, generating respectively the tones C2, C2i, D2 B2. In a similar manner, a series of generators 18, covering a third octave is connected to the gating circuits 1, 2, 3, 12. These generators are indicated respectively as C3, G3i?, D3 B3. Other octave groups may be connected in a similar manner, if so desired.

As will be discussed in detail in a subsequent paragraph, the gating circuits 1, 2, 3, 12 include key switches (not shown) which may be playing-key operated, and which supply, via output leads 2li, 22, 24,

26, tone signals (corresponding to the notes selected by the key switches) to an outbut bus 28. Leads 3i), 32 and 34 are connected to the output bus 2S and convey the signals to appropriate tone `color circuits 36, 38 and 40 respectively. By means of stop switches 42, 44 and 46, the outputs of the tone color circuits 36, 38 and 40 may be selectively applied-to an appropriate output system 48, which may be a conventional amplier and loudspeaker system;

As will be explained in greater detail in connection with FIG. 2, D.C. supply sources 5t), 52 and 54 may be connected as shown to the gating circuits 1, 2, 3, 12.

It will be readily understood by one skilled in the art that only tone signals which are harmonically related pass through each gating circuit 1, 2, 3, 12.

Referring now to FIG. 2 for the detailsof the gating circuits 1, 2, 3, 12, there is indicated by the dotdash line 56 a block which corresponds to the gating circuit of FIG. 1. It will be seen that input signals corresponding to the notes C1, C2 and C3 are brought Vinto the gating circuit through appropriate leads to respective keying circuits indicated generally as 58, 60 and 62. Entry is made to the keying circuit 58 by way of capacitance 64 to a branch point -65 from which signals are carried via resistor 66 and neon tube 68 to a bus 70. ln a similar manner signals from the C2 and C3 generators are brought into keying circuits 60 and 62.

To the branch point of keying circuit 58 is also connected a resistor 72 in series with a capacitor 74 and switch 97 to a common return 76, indicated as ground. Also, one terminal of a key switch 75 is connected to a point between resistor 72 and capacitor 74.

VThe other terminal of the key switchfis connected to a bus S0 which carries +160 volts from a supply source indicated at 50 in FIG. l. It will be understood that the switch 78 is operated by a playing key of the instrument (not shown). In a similar manner the notes C2 and C3 may be keyed through keying circuits 60 and62 by key switches 82 and 84 respectively. If so desired, additional keying circuits for further harmonically re- 12AX7. The output from the cathode of tube 86 is carried through a decoupling resistor 96 to the output lead from which notes C1, C2 and C3 may be derived in output header 28 (FlG. l) as determined by the operation of the key switches 7S, S2 and 84 respectively. Y The gating circuits 2, 3, 12 may be constructed in detail similar to that of gating circuit 1. An exemplary set of values for keying Vcircuit 1 is indicated on the various components connected therein. These values are exemplary only and, as will be lobvious to one skilled in the art, may be varied to suit the needs of specic circuitry.

As is well known in the art, tone color circuits 36, 3S and 40 (FIG. 1) may be low-pass, high-pass or other appropriate filters as desired to meet the voicing needs of the particular instrument. Y

The operation of the gating circuit (FIG. 2)Y will now be explained. The positive bias of 4.5 volts on the cathode of tube S6 renders the tube cut-ott` when none of the key switches 73, 82 and 84 is operated. Thus feedthrough from the signal sources C1, C2, and C3, which may bey present on bus 70 as a result of the stray capacitance between the electrodes of neon tubes such as 68, is prevented from passing through to the 'output system. However, if, for example, the key switch 78 is operated, the signal from the C1 generator is passed through the neon tube 68 to the cathode follower tube 86 in a manner which will be explained in detail hereinafter. The output of the switching circuit 58, carried via the neon tube 68, is a positive-going signal which overcomes the cut-olf bias of the cathode follower tube 86 and is passed on via the resistor 96 to the output of the instrument. Y

The manner in which tone signals getrthrough a keying circuit, such as indicated at 5S, will be understood as follows: A voltage from the C1 generator, of relatively large saw-tooth wave form, is applied to the tube 68 via capacitor 64 andV resistor 66. This voltage is not high enough to cause a discharge in the gas in the tube 68. However, when the switch 78 is closed, the VDC. voltage on the bus is superimposed upon the generator signal applied to the tube 68 and the latter fires, allowing the signal to pass through to the grid of tube S6. Capacitor 64 has two functions in the circuit. lt not only serves as a coupling capacitor or the generator signal, but also serves to limit the rate at which: the D C. voltage buildsy up across the'tube 68. This allows the attack of the tone to be controlled by choice lated notes may be connected in a similar manner to the Y buses 70- and 80. f

Connected to the bus 70 of the gating circuit 1 of FIG. 2, is a common gating valve circuit composed of a vvacuum triode 36, the grid of which has a connection to the bus 73 by way of lead 88. VThe tube 86 may be connected in a conventional 'manner as a cathode fol-V lower with a Vgrid resistor 90, a cathode resistor 92 and a capacitor 94 which was found to improve operation of the circuit. Plate supply for the tube 86 may be +90 volts (for a rIype 12AY7) connected as shown, and may be derived from a power supply such as indicated at 52 `in FIG. l. The tuber86 is biased at its cathode from a source such as 54 in FIG. l, which is preferably at +45 volts, as indicated in FIG. 2, if tube 86 is Type percussive-tone producing instrument,

of a suitable value for capacitor 64.

When the key switch 7S is released, the charge built up on the capacitor 74 will decay at a rate determined by the resistors 72 and 66 plus that of the grid resistor 90 connected to the tube 86. With the exemplary values shown, the decay is a gradual one, simulating that of a when the key switch is played in a.staccato manner. Y

In the event that the system described .in connection with FIGS. 1 and-2 is tobe used as a general gating system for a division of an organ in which percussiveV effects may sometimes be desired and sometimes not desired, means for eliminating the gradual decay of the tones may be found advisable. ln the light of the explanation given above, if in any keying circuit such as the circuit 58, the effect of the .capacitor '74 is eliminated, the gradual onset of the tones will be preserved, but there will be no such gradual decay as would produce a percussive effect. The virtual elimination of capacitor 74 is easily accomplished by breaking its connection with ground or the common return. To this end there is illustrated in FIG. 2 a plurality of switches 97, 98 and 99 located between capacitor 74 and its counterparts and ground. These switches may form part of a multi-contact switch or relay switch (as indicated by the dotted lines) which will be operated vby a stop tab.

It will be understood that -two'or more notes maybe i to an output header 123.

played through the same cathode follower without producing intermodulation distortion, since frequencies are octavely related.

It will be understood that when one note is being played and the cathode follower tube 86 is passing the signal corresponding thereto, any feed-through fromother keying circuits, for example 60 and 62, will not be noticeable, since its components will be harmonically related to the signal C1 which is being keyed.

Thus it will be clear to one skilled in the art upon reading these specifications that there has been provided a new and improved gating system for an electronic musical instrument, which is low in cost, satisfactory in operation and otherwise meets the objects of the invention as set forth hereinabove.

It will be further obvious to one skilled in the art that the circuits described above are purely exemplary. If desired, other voltage-responsive devices may be employed in the place of the neon tubes, for example, a semi-conductor diode, which will be non-conductive until a D.C. potential of appropriate value is supplied thereto. There may further be used in the place of the gating valve circuit which includes tube 86, a semi-conductor valve circuit employing a transistor or diode of appropriate characteristics, such that it is cut-off until a pulsating signal large enough to overcome the cut-off bias is supplied to it by means of keying circuits such as 58, or any other keying circuit within the spirit of this invention. An example of a biased vacuum diode used as a gating valve is illustrated in FIG. l of U.S. Patent 2,483,823 to George.

Appropriate keying circuits of the type illustrated in the copending application Serial No. 4,444 may if desired be employed. The preferable condition for such keying circuits is that the output be in the form of a pulsating D.C. signal such that the gating vaive 86 in FIG. 2 will be unblocked by the keyed signal.

FIG. 3 illustrates a way in which the gating circuits of this invention may be employed in lieu of gradual contact or resistive switches in an organ division, with provision for those modes of voice derivation which are set forth in the Kock patent above referred to. In FIG. 3, which is a partial circuit diagram, three oscillators have been shown marked respectively C1, C2 and C3. The outputs of these generators are connected through leads 100, 101 and 102 to keying circuits here designated as [03, 104 and 105. These keying circuits feed a gating valve circuit 106 as hereinabove described which is connected to a header 107 marked as an 8 header.

In FIG. 3 the generators are shown as having branch circuits 108, 109 and 110, which circuits may be re garded as circuits enabling the use of oscillations produced by the generators on some different manual or division of the organ, as is usual in this art. The generator C2 has a branch circuit 111 connecting it with a keying circuit 113. Similarly the generator C3 has a branch circuit 114 connecting it with a keying circuit 116.

The keying circuits 113 and 116 form part of a second gating system. They are shown connected together and to a gating valve 117 the output of which is connected to a header 118 which may oe termed a 4 header. If the i key switch in keying circuit 103 and the key switch in the keying circuit 113 are both arranged to be actuated by the same playing key of the instrument, it will be evident that oscillations from generator C1 will be derived in header 107 while oscillations from C2 will be derived in header 118. The arrangement thus described can be continued throughout the gamut of the keyboard of the instrument utilizing the circuit arrangement of FIG. 3.

This figure also shows a pair of tone color lters 119 and 120 connectable by tone color switches 121 and 122 The switches just mentioned will of course be operated by stop tabs or the like; and the tones derived in the output header 123 from the tone color devices 119 and 120 will be 4 tones. Another exemplary tone color filter 124 having a stop tab switch 6 125 is shown as connected between the header 107 and the output header 123. The tones derived through the filter 124 will be 8' tones. Another filter 126 is shown as connected both to header 107 and to header 118, and to the output header 123 by a stop switch 127. The filter 126 will pass portions of both the 8 and 4 oscillations and therefore may be referred to as a mixed tone color filter. Yet another tilter 128 is shown as connected directly to header 107 and to header 118, the latter connection including an outphasing means 129, as taught in the said Kock patent. When the stop switch 130 is closed tones will be derived in the output header 123 from the tone color filter 128 in which tones the odd-order harmonics are accentuated -to give superior Woodwind etects. On the other hand the tone color filter 126 will transmit a tone of a type in which the second harmonic is accentuated, which tone is appropriate for diapason effects. The header 123 is shown as connected to an output system 131, which may be thought of as comprising an amplifier and one or more loudspeakers, although other apparatus may be included. While FIG. 3 shows the derivation of 8 and 4 tones in different headers through the use of two banks of gating circuits, it will be understood that by extending these teachings other headers may be established `for other footages. The arrangement of FIG. 3, whether extended or not, is especially adapted to the use of the gating circuits herein taught for obviating gradual contact or resistive key switches, whether or not percussive effects are provided for; but as indicated above it is an advantage of the gating circuits of this invention that percussive effects are readily obtainable when desired.

In FIG. 4 certain generators marked respectively C1, C2, G2, C3 and G3 are shown representative of the generators in a generator rank. FIG. 4 is illustrative of the fact that special effects may be obtained by connecting more than one generator to the various keying circuits forming a part of a gating circuit bank. Particularly for percussive elfects, the accentuation of certain harmonics may be desired, as in reproducing the tones of chimes, bells and the like.` It will be observed in this iigure that keying circuit 132 has connection with generators C1 and C2 and G2, the connections including the usual isolating resistors. Keying circuit 133 has connection with generators C2, C3 and G3. Keying circuits 132 and 133 feed a gating valve 134 which in turn feeds a header 135. This header will contain a mixture of oscillations derived from several generators; and while for illustrative purposes the fundamental and the second and third harmonics have been chosen, it will be understood that other ha-rmonic combinations may be selected as desired. It will also be understood that keying circuits 132 and 133 together with gating valve 134 form a part only of a bank of gating circuits as hereinabove described. Since the outputs of several generators are shown as connected together before being connected to the keying circuits, it will be understood that mixtures of oscillations will be derived in the header 135 upon the actuation of a single key switch in keying circuit 132 or keying circuit 133.

For other uses in the same division of the organ there may be one or more additional gating circuit systems. In FIG. 4 a second system has been partially shown comprising keying circuits 136, 137 and 138 each havinga single connection, with generators C1, C2 and C3 respectively. These last mentioned keying circuits feed a gating valve 139 which in turn feeds a -header 140. Various tone color filters have been indicated at 141 and 142 connected through stop switches to a header 143 which feeds an output system 144. The tone color filters 141 and 142 are connected between the output header 143 and headers 135 and 140 respectively. It will beunderstood that the system paltially illustrated in FIG. 4 may be elaborated in accordance with FIG. 3 by the addition of one or more gating circuit banks so as to derive octavely or otherwise harmonically related oscillations in additional headers 5, such as 16', 4, 2 headers and the like. In the modifications illustrated in FIGS. 3 and 4 the advantage of the gating circuit systems of this invention, in doing away with feed-through will be maintained because the various gating valves will be transmitting only harmonically related oscillations.

The gating circuit systems or assemblies of this invention are relatively simple and inexpensive. There will be, of course, a keying circuit for each semi-tone throughout the gamut of any keyboard or portion thereof to which the gating circuit system is applied. But a single gating valve will take care of the harmonically related oscillations derived from octavely related generators as in FIGS.Y

l, 2 and 3 and such octavely related oscillations plus other harmonically related oscillations in FIG. 4. Regarding a plurality of keying circuits and a gating valve as one unit in the system, it will be seen that each gating system will comprise only twelve such units. The cost of a gating system as such is not necessarily higher, may be lower than the cost of a set of gradual Contact or resistive switches, and will not be subject to physical wear. A series of gating circuit systems for such purposes as are illustrated in FIGS. 3 and 4, by the sarne token, are not necessarily more expensive than corresponding gangs of gradual contact or resistive switches. If in any gating circuit system the effect of percussion is not desired, capacitor 74 and those corresponding to it in other keying circuits may simply be omitted. In some instruments on any given keyboard, one gating circuit system may be reserved for percussive effects, while another or others are used for regular organ tones. For example, if the keying circuits 132 and 133 of FIG. 4 employ capacitors, such'as taught in FIG. 2 at 74, a percussive voice may be available in output system 144, as modified by the tone color filter 141, while a regular organ voice may be available via keying circuits 136, 137 and 138, gating valve 139 and tone color iilter 142, previously described. As taught by Bissonette and Kramer in a copending application Serial No. 621,769, filed November v13, 1956, and entitled Electronic Musical Instrument, belonging to the same assignee, a regular voice may be employed along with a percussive voice to effect a more complex onset to the percussive tone, that is, during the key-down portion of the tone. Y

Where, from any individual gating circuit system both percussive tones and ordinary organ tones are alternatively desired, use may be made of the multi-contact switches (operated by a stop tab directly or through the intermediary of a relay) as hereinabove taught.

Although it has been stressed herein as preferable to employ keying circuitsV which provide a comparatively gradual onset to the organ tones (that is free of pops), the teachings of this invention relating to keying of harmonically related oscillations through a common gating valve may also be applied to simple make-break or variable resistance keying circuits, if, for example, signal feed-through `due to switch capacitance is a problem. In such usage the keying circuits illustrated in'FIG. 2 are replaced respectively by direct contact switches and appropriate isolating resistors between the sources (such as C1, C2, C3) and the gating valve 86.

The gating circuit systems of this invention are excellently adapted for kit-installation in already-existing instruments.

It is an advantage of the gating circuit systems herein described that whereas the inherent cost of prior percussive systems has in many instances dictated the conining of the percussive effect to some selected portion of a single keyboard, percussion for additional notes in the present invention entails little added cost since it does not require additional gating valves but only additional keying circuits.

YModifications may be made in the invention without departing from the spirit of it. Y

The invention having been described in certain exemii plary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. In an electrical musical instrument of the type having a gamut of continuously operating tone signal sources extending over a range of at least two octaves, a plurality or" selectively operable keying circuits having input terminals'respectively coupled to said sources, each of said keying circuits having substantial inherent feed-through of tone signal when non-conductive, said keying circuits having each an output terminal, collector means for tone signals derived from said keying circuits, Vand a load circuit coupled to said collector means, the combination o a gating system comprising a plurality of gating means normally in non-conductive condition and capable of substantially completely attenuating said feed-through when inthe non-conductive condition, each gating means having an output terminal coupled to said collector means and an input terminal coupled to the output terminals of only harmonically releated ones of said keying circuits, means responsive to application of any one of said tone signals to any one of said harmonically related keying circuits for rendering its gating means conductive, whereby when any one gating means is conductive, only feed-through to said load circuit of harmonically related tones can exist through the conductive gating means.

2. A system according to claim l, and further including means interposed between said tone signal source and the input terminals of said keying circuits for combining the outputs of harmonically related ones of said tone signal sources for application to said keying means.

3. A system according to claim 1, wherein each gating means includes a unilateral control device as a gating element, said device having a control electrode.

4. An electrical musical instrument according to claim 1, wherein is further provided a second gating system including keying circuits, gating valves and a further collector means and means coupling said sources of tone signals respectively through said first and second gating systems rto said rst mentioned and further collector means such that tone signals of dierent footages are derived in said irst mentioned and further collector means, respectively.

5. A gating system for'an electrical musical instrument, comprising a series of sources of tone signal, said sources of tone signal encompassing at least two octaves of the musical scale, a load circuit, means for selectively gating said tone signals into said load circiut, said last means comprising a separate diode circuit in series with each of said tone sources, said diode circuit being all normally non-conductive, key responsive means for at willY rendering said' diode circuits selectively conductive to pass said tone signals, a normally non-conductive gate permanently connected at all times between a plurality of said'diode circuits and said load circuit, the diode circuits pertaining to and connected to each of said gates being connected to sources of only harmonically related tone signals, and means for rendering each of said gates conductive in response to rendering conductive of any one or more of the diode circuits connected'thereto, said keying circuits being subject to substantial feed-through of said tone signals when non-conductive, said gates being subject to substantially no feed-through of said tonersignals when non-conductive.

6. A gating system for an electrical musical instrument, comprising a series of sources of tone signal, said sources of tone signal encompassing at least two octaves of the musical scale, a load circuit, means for selectively gating said tone signals into said load circuits, said last means comprising' a keying circuit in series with each of said tone sources, said keying circuits being normally non-conductive, key responsive means for at will rendering said keying circuits selectively conductive to pass said tone signals, a normally non-conductive gate connected at all times between a plurality of said keying circuits and said load circuit, the keying circuits pertaining to and connected to each of said gates being connected to sources of only harmonically related tone signals, and means for rendering each of said gates conductive in response to passage of a control signal deriving from any of the keying circuits connected thereto, said keying circuits being subject to substantial feed-through of said tone signal when non-conductive, said gates being substantially impervious to said feed-through when non-conductive.

7. A gating circuit comprising a `source of alternating current signal, a rst diode gate in series with said source of alternating current signal, a further source of alternating current signal, a further diode gate in series With said further source of alternating current signal, another gate, means connecting said another gate in cascade with both said diode gates taken in parallel, means normally biasing ot said another gate, a source of gating voltage, iirst key means for at will connecting said source of direct current gating voltage to said tirst diode gate, second key means for at will connecting said source of direct current voltage to said second diode gate, each of said diode gates being rendered conductive in response to said direct current Voltage and passing both said direct current voltage and said alternating current signal, and means to render said `another gate conductive to said alternating current signal responsive to said direct current voltage passed by any one of said diode gates.

8. A gating circuit comprising a source of alternating current signal, a keying circuit in series with said source of alternating current signal, a further source of alternating current signal, a further keying circuit in series with said further source of alternating current signal, another gate, means connecting said another gate in cascade with both said keying circuits taken in parallel, means normally biasing said another gate into non-conductive condition, a source of direct current gating voltage, first key means for at will connecting said source of direct voltage to said first keying circuits in on-gating relation, second key means for at will connecting said source of direct current voltage in on-gating relation to said second keying circuit, each of said keying circuits when conductive passing said direct current voltage and said alternating current voltage, and means applying said direct current voltage to bias said another gate into conductive relation to said alternating current signal when said direct current voltage is passed by either of said keying circuits.

9. A gating circuit, comprising a plurality of tone signal sources encompassing at least two octaves of the musical scale, a separate keying means in cascade with each of said sources, said keying means having inherent feedthrough of said tones when non-conductive, a gate connected with plural keying means, said last named keying means being connected only to harmonically related tone signal sources, said gates being normally non-conductive and being subject to substantially Zero inherent feed through of said tones when non-conductive, and means responsive to closure of any of said keying means for rendering the gate in cascade therewith conductive, whereby said gate when conductive passes a tone and only feedtiirough tones which are harmonically related to that tone.

10. The combination according to claim 9 wherein said keying means are diode gating circuits.

11. The combination according to ciaim 9 wherein said gates include unilateral control gating devices.

12. A gating circuit comprising a normally non-conductive diode keying circuit, a further gate in cascade with said diode keying circuit, a source of direct current keying voltage, said keying circuit being rendered conductive responsive to application thereto of said direct current keying Voltage, means for at will applying said direct current keying voltage to said diode keying circuit, means normally biasing said further gate to non-conductive condition, and means responsive to application of said direct current key voltage to said keying circuit for further applying said direct current voltage via said diode keying circuit to bias said gate into conductive condition.

13. The combination according to claim 12 wherein said source of direct current keying voltage includes a source of unvarying direct current voltage, a switch and a capacitor, means responsive to closure of said switch for connecting said capacitor across said source, and a circuit for applying the voltage of said capacitor to said diode keying circuit as said direct current keying voltage, said circuit including a slow discharge resistance for said capacitor.

References Cited in the tile of this patent UNITED STATES PATENTS 2,458,178 Langer Jan. 4, 1949 2,481,608 McKellip Sept. 13, 1949 2,562,670 Koehl July 31, 1951 2,577,753 Hanert Dec. 11, 1951 2,579,358 Boum Dec. 18, 1951 2,757,280 Beard July 31, 1956 2,811,887 Anderson et al. Nov. 5, 1957 2,819,640 Anderson Ian. 14, 1958 2,835,829 Sourgens et al. May 20, 1958 2,891,171 Shockiey June 16, 1959 2,918,576 Munch Dec. 22, 1959 2,986,964 Bissonette et al iune 6, 1961 FOREIGN PATENTS 747,873 Great Britain Apr. 18, 1956 OTHER REFERENCES Richter: Fundamentals of Industrial Electronic Circuits, McGraw-Hill, 1947 (pages 410 and 414 relied on), 

9. A GATING CIRCUIT, COMPRISING A PLURALITY OF TONE SIGNAL SOURCES ENCOMPASSING AT LEAST TWO OCTAVES OF THE MUSICAL SCALE, A SEPARATE KEYING MEANS IN CASCADE WITH EACH OF SAID SOURCES, SAID KEYING MEANS HAVING INHERENT FEEDTHROUGH OF SAID TONES WHEN NON-CONDUCTIVE, A GATE CONNECTED WITH PLURAL KEYING MEANS, SAID LAST NAMED KEYING MEANS BEING CONNECTED ONLY TO HARMONICALLY RELATED TONE SIGNAL SOURCES, SAID GATES BEING NORMALLY NON-CONDUCTIVE AND BEING SUBJECT TO SUBSTANTIALLY ZERO INHERENT FEED THROUGH OF SAID TONES WHEN NON-CONDUCTIVE, AND MEANS RESPONSIVE TO CLOSURE OF ANY OF SAID KEYING MEANS FOR RENDERING THE GATE IN CASCADE THEREWITH CONDUCTIVE, WHEREBY SAID GATE WHEN CONDUCTIVE PASSES A TONE AND ONLY FEEDTHROUGH TONES WHICH ARE HARMONICALLY RELATED TO THAT TONE. 